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Date: Tue, 15 May 2018 08:41:57 -0700
From: Fenghua Yu <fenghua.yu@intel.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
        "H. Peter Anvin" <hpa@linux.intel.com>,
        Ashok Raj <ashok.raj@intel.com>,
        Ravi V Shankar <ravi.v.shankar@intel.com>,
        Tony Luck <tony.luck@intel.com>,
        Rafael Wysocki <rafael.j.wysocki@intel.com>,
        Arjan van de Ven <arjan@infradead.org>,
        Alan Cox <alan@linux.intel.com>, x86 <x86@kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 01/15] x86/split_lock: Add CONFIG and enumerate #AC
 exception for split locked access feature
Message-ID: <20180515154156.GA244301@romley-ivt3.sc.intel.com>
References: <1526323945-211107-1-git-send-email-fenghua.yu@intel.com>
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 <3194fef3-68a7-327b-395b-a98bbb12e40a@intel.com>
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On Tue, May 15, 2018 at 08:36:35AM -0700, Dave Hansen wrote:
> On 05/14/2018 11:52 AM, Fenghua Yu wrote:
> > +#include <linux/printk.h>
> > +#include <asm/msr.h>
> > +
> > +static bool split_lock_ac_supported;
> 
> Was there a reason not to use an X86_FEATURE* bit for this?

The feature is not enumerated in cpuid. It's detected by writing 1
to bit 29 in MSR 0x33.

So it can't fit in X86_FEATURE, right?

Thanks.

-Fenghua